// This program finds the distribution of leading nonzero digits in a set of
// numbers.  The program is useful for exploring the phenomenon known as
// Benford's Law.  It simply ignores tokens that don't have a nonzero digit in
// them, so you can feed it input files that have extra text like labels.

import java.io.*;
import java.util.*;

public class Benford {
    public static void main(String[] args) 
            throws FileNotFoundException {
        Scanner console = new Scanner(System.in);
        System.out.println("Let's count those leading digits...");
        System.out.print("input file name? ");
        String name = console.nextLine();
        Scanner input = new Scanner(new File(name));
        int[] count = countDigits(input);
        reportResults(count);
    }

    // Reads integers from input, computing an array of counts
    // for the occurrences of each leading digit (0-9).
    public static int[] countDigits(Scanner input) {
        int[] count = new int[10];
        while (input.hasNext()) {
            int n = firstDigitOf(input.next());
            count[firstDigit(n)]++;
        }
        return count;
    }

    // returns the first nonzero digit of a string, 0 if no such digit found
    public static int firstDigitOf(String token) {
        for (char ch : token.toCharArray()) {
            if (ch >= '1' && ch <= '9') {
                return ch - '0';
            }
        }
        return 0;
    }

    // Reports percentages for each leading digit, excluding zeros
    public static void reportResults(int[] count) {
        System.out.println();
        if (count[0] > 0) {
            System.out.println("excluding " + count[0] + " tokens");
        }
        int total = sum(count) - count[0];
        System.out.println("Digit Count Percent");
        for (int i = 1; i < count.length; i++) {
            double pct = count[i] * 100.0 / total;
            System.out.printf("%5d %5d %6.2f\n", i, count[i], pct);
        }
        System.out.printf("Total %5d %6.2f\n", total, 100.0);
    }

    // returns the sum of the integers in the given array
    public static int sum(int[] data) {
        int sum = 0;
        for (int n : data) {
            sum += n;
        }
        return sum;
    }

    // returns the first digit of the given number
    public static int firstDigit(int n) {
        int result = Math.abs(n);
        while (result >= 10) {
            result = result / 10;
        }
        return result;
   }
}